This disclosure relates to devices for performing assay procedures utilizing separation processes, and, more particularly, to a filtration apparatus having a plurality of sampling wells and a method of assembling the same.
Individual and multi-well filtration and titration apparatuses are utilized in a variety of biological and chemical and industrial assay procedures. In such procedures, a sample can be collected on a filter medium for subsequent analysis, or an impurity can be removed from a liquid by being collected on a filter medium and the filtrate collected and analyzed. In either case, various methods exist by which the filter medium can be maintained in position in the sampling well.
One such method includes compression-fitting the medium in the well, which may enable a sample to seep between the compression-fitted surfaces. In an application in which an analysis of filtered sample retained on the membrane is made by a visual method (e.g., luminometry, fluorescence), some of the sample may escape detection, thereby causing the final analysis to be inaccurate. Another method of maintaining the filter medium in place includes bonding a unitary piece of filter medium material at the rim edges of adjacently positioned wells with heat or adhesive or by ultrasonic welding. Because the portions of the filter medium that correspond to each well are in physical communication with each other, the possibility of “cross-talk,” or fluid communication between each well through the filter medium material, exists and poses a cross-contamination threat. A third method of assembly requires the upper well plate and the lower plate to be used as a punch and die in the cutting of discs from a unitary sheet of membrane placed between the plates and a secondary step of bonding the upper and lower plate thereby encapsulating the membrane. This method relies on extremely high tolerance injection molded upper and lower plates relative to well centers and has limitations relative to the media which can be cut. Since the filter material is not discretely separated during the manufacturing of the apparatus, there remains the probability of cross-talk between wells of the multiwell filter device. In applications in which contamination between wells occurs, false or inaccurate sample readings may be obtained. Another method incorporates the inserting of a lower plate containing discs of material into an injection mold and the insitu molding of an upper plate into the lower plate. In this technique, no compensation is provided for the differential shrinkage between the inserted lower plate and the upper plate molded around or into it. This leads to a substantial internal stress, which can cause warpage, and stress cracking. Therefore there are numerous limitations in terms of material selections, product design and flatness tolerances.
What is needed in the art is a filtration apparatus that retains a discrete filter medium element securely in a sampling well while reducing the potential for obtaining inaccurate sample readings and eliminating the potential for cross-contamination in a wide selection of filter media, materials of construction, and design configurations.